This study analyzed the causes, types, administrative measures taken and suggestions concerning medication errors according to the perspective of professionals involved with the medication systems in four Brazilian hospitals. It is an exploratory, survey-type, multicentric study. The sample consisted of professionals from the medical clinic and pharmacy in the above-mentioned hospitals. Semi-structured interviews were used for data collection. Results showed that the most frequently error types mentioned by the professionals were related to medication ordering/transcription. Lack of attention, individual mistakes and problems in service management were the major causes of errors. Reports were the main measures taken in view of errors, and changes in individual attitudes were the most frequently mentioned form to prevent them.